The synthesis of various heterometallic oligomers containing iron and molybdenum or tungsten has been accomplished. Specifically the complex anions ((SC6H5)2FeMS4)2-, (M equals Mo, W); ((S5)FeMS4)2-, (M equals Mo, W); (Cl2FeMS4)2-, (M equals Mo, W) and ((Cl2Fe)2MS4)2-, (M equals Mo, W) have been characterized and their crystal and molecular structures have been determined. The reactions of these molecules, and of the recently synthesized and structurally characterized ((MoS4)2Fe)3-complex are being examined in detail. Emphasis is placed on the synthesis of aggregate with the 6:1 Fe:Mo ratio reported for the nitrogenase cofactor. Concommitant with these studies, the synthesis of polypeptides containing four cysteinyl residues, has been accomplished. These peptides are used as "ligands" in ligand substitution reactions with the complexes reported previously. The properties of these peptide "complexes " are under investigation.